Extruders and ring rollers are devices for plastic shaping of materials, for example preheated heavy-metal or light-metal ingots, by a selective application of force. Thus, in the case of an extruder, for example, such a heavy-metal or light-metal ingot, also termed billet, is driven by a hydraulically operated press ram through a so-called die, whereby a semi-finished product with a specific defined profile is produced. Such extruders are evident from, for example, DE 38 36 702 C1 and DE 10 2012 009 182 A1 [US 2015/0090132].
Apart from the actual application of force for shaping the workpiece, plants of that kind typically have drives for moving or positioning the receiver with the die or other plant components. The ingot receiver is typically configured by hydraulic cylinders over large strokes and brought into position. Thus, for example, the receiver is moved in this way between a position for ingot change and a front end position, i.e. the work position, at which sealing or pressing against, ventilating and stripping take place. Alternatively, use is made of electric motors which move the receiver between the ingot change position and the work position.
In the case of use of electric motors, internal forces of the hydraulic cylinders have to be overcome. This applies particularly to the use of double-rod rams in which due to the mode of construction thereof, i.e. two guided piston rods plus pistons, in a given case hollow-cylinder pistons, it is necessary to overcome, apart from flow losses, relative mechanical friction forces. On the other hand, double-rod rams are useful in the discussed shaping apparatuses, since they can be converted over the entire stroke thereof from towed operation to work operation.